Most semiconductor fabrication systems, particularly thermal and plasma chemical-vapor deposition (CVD) reactors, must provide good process uniformity (including temperature uniformity, reactant species uniformity, deposition uniformity, and mass transport uniformity) when performing substrate processing. Conventional CVD systems typically use single-zone showerheads (or rings) in order to inject the process gases/vapor into the process chamber for wafer processing.
In a conventional showerhead design, the injector plate has an array of holes operating to inject a single gas or a combination of process gases into a deposition chamber or process environment in an attempt to provide a uniform mass transport of reactant flux to the wafer or substrate. These conventional showerhead designs can be referred to as single-zone showerheads because these "single-zone" showerheads only control flow of process gases through the showerhead (i.e., within one zone equal to the showerhead itself), without any multi-zone spatial control over the gas flow distribution uniformity over the substrate.
Such conventional single-zone injectors experience problems meeting the process uniformity and cleanliness requirements for various deposition processes due to the problems associated with pre-mixing and gaseous phase reaction of the process gases and also due to lack of multi-zone control over the mass-transport uniformity profile. Typically CVD systems use multiple process gases to deposit a film onto a work piece. The multiple gases may consist of a combination of a precursor gas or vaporized liquid and a carrier gas or multireactant gases. In conventional single-zone showerhead designs, the multiple gases are premixed within the showerhead assembly or prior to delivery to the showerhead assembly before injection into the process chamber. The process of premixing multiple gases can result in gas-phase nucleation which can, in turn, result in generation of particulates and process contamination causing manufacturing yield degradation. Particulate generation represents a serious problem because CVD applications require a clean environment.
These prior art designs are also limited because the single-zone designs do not provide a capability for spatial control of the reactant species concentration (mass transport uniformity) profile. The non-uniformity in the reactant species concentration over the wafer will result in non-uniform film thickness and/or quality.
Another limitation in conventional showerhead designs is the lack of the ability to clean the showerhead surface in-situ, without opening up the chamber.